Downgrading help

[darkeh]

hi all

A friend of mine bought an CYMA MP5K but it was chrono'd at 360 where the site we play at is 330.

We are trying to just put a lower spring in but when we put an m105 spring in the fps dropped to 140! The m105 is longer than the stock spring. Also I noticed the gun had a ported cylinder. This apparently helps increase fps for short barrels. Now the main question is that the ports on the cylinder are tear dropped shaped (>

Does it matter which way round the cylinder is? I.e the thin end of the teardrop nearer the front?

I'm still new to tinkering with AEGs so advise would be appreciated.

Phil

[colinjallen]

Re: Downgrading help

They are normally fitted with the narrower end of the port towards the barrel. As it is an MP5K, I assume that the port is half way along the cylinder. However, such a large power drop seems excessive and sounds more like you now have an air seal problem.

[Shizbazki]

Re: Downgrading help

I would say the drop in FPS is down to an Air Seal issue around the piston head and cylinder not making a full seal and therefore you are losing air pressure.

Dissassemble the weapon, open the GB take out the piston + head, use some petroleum free silicone grease and grease up the piston o-ring and the inside of the cylinder, make sure that the cylinder head is also air tight (use PTFE tape around the heads rubber ring), if there are any ports on the cylinder these go to the rear normally.

Install the spring with the tightest coils to towards the spring guide if the spring is non linear, also test the air seal and compression, put it back together and see what you get.

More detail might help us as there are several reasons why FPS drops so much but its normally an Air seal issue

[darkeh]

Re: Downgrading help

Cheers for the advise guys - turns out the cylinder was in back to front.... (i didnt take it apart originally) but with your explanations it certainly made sense and i learnt more so a big thanks

Phil

[colinjallen]

Re: Downgrading help

Good to hear you got it sorted. Someone is a muppet for putting the cylinder in the wrong way round.

[darkeh]

Re: Downgrading help

Yeah that was me lol I'm still learning


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